Marcellus Shale is a sedimentary rock buried thousands of feet beneath the earth’s surface. It stretches from upstate New York south through Pennsylvania to West Virginia and west to parts of Ohio. Named after a town in upstate New York, the rock itself is millions of years old, formed from mud and organic material. The natural gas created over millions of years as a byproduct of decomposition is trapped in tiny spaces and fissures within the rock. The Marcellus Shale is just one of many shale formations across the world. When industry speaks of tapping shale gas, it often refers to it as a “shale play.” The Marcellus is one of the first shale plays to be tapped, after the Barnett Shale formation in Texas.